Centrifugal pump



July 28, 1942. 5;, LA BOUR I 2,291,478

CENTRIFUGAL PUMP Filed Aug. 12, 1939 4 Sheets-Sheet 1 Mania" Ja -28,1942. W

H. E. LA BOUR camm'uw. runr Filed Aug 12, 1939 4 Sheets-Sheet 2 July 28, 1942. H. E. LA. BOUR CENTRIFUGAL PUMP I Filed Aug. 12, 1939 4 Shets- Sheet 3 Patented July 28, 1942 UNITED STATE cENTmFUGAL PUMP Harry 1:. La an, Elkhart, Ind. Application August 12, 1939, Serial No. 289,757

8 Claims. (01. 103-103) Y My invention relates to centrifugal pumps and more particularly to that type of centrifugal pump wherein there is an open impeller which operates in a concentric pumping channel and the impeller blades sweep type may be designated as the concentric type.

Since any centrifugal pump consists essentially the channel; This s of only one moving part, that is, the impeller, and

size and cost of the pump and of its driving.

motor.

The present invention is peculiarly applicable to self-priming centrifugal pumps. Self-priming centrifugal pumps have two inherently conflicting requirements, namely, rapid and efficient air removal during priming and efficiency and effectiveness in liquid pumping. The first phase relates to pumping, air and the second phase to pumping liquid, which is usually about 700 times as heavy. In prior designs it has generally been the case that one function has had to sufier in order to secure improvement in the other. The present invention removes, in large part, the limitations of known designs and allows of a marked increase in efficiency and delivery in liquid pumping'while retaining the air-handling abilities of the best prior art constructions. The principle of the present invention releases the designer from prior limitations.

The basic concept of the present improvement in centrifugal pumps of the aforesaid known types is to deliver into the throat or. throats liquid at maximum pressure only and to prevent, as much as possible, thedelivery of liquid atiess than maximum pressure. In other words, each impeller blade is to be caused to deliver into the throat liquid at the highest mean pressure that the pump is capable of delivering for the particular demand made upon it, that is, the rate of delivery. How this concept is realized will now be disclosed by reference to what goes on in a pump of this class.

I have analyzed the operation of a pump of this type as follows:

Assume a concentric pump with the discharge closed off and the impeller rotating at the rated speed. The liquid between the vanes is now whirled like a flywheel. It is prevented from flying apart or outwardly not by its own coherence, as in a metal flywheel, but by the concentric restraining walls of the channel and pumping chamber. The force of a particle at any particular radius, tending to discharge tangentially (that is. out through a tangential discharge port), is a function of the square of the radius. This is known. Each particle retains its position by virtue of the opposing forces which restrain it. The inertia of motion-the inherent energy which it possesses-tends to make a particle continue in a straight line. The curved channel walls exert an inward force which cause the particle to move in a curved path.

Considering the circular mass of liquid as made up of successive concentric cylindrical laminae, the outermost layer has maximum velocity because it lies at the outermost radius, and it has inherent energy proportional to its mass and the square of its velocity.

Now as the discharge is opened up, it is apparent that the theoretically perfect pump will cause the outermost laminae to be discharged as an outflowing ribbon of an aggregate rate of how exactly equal to the rate of flow of the permitted discharge. This would supply the discharge for each value at the highest'possible effectiveness and pressure. As the discharge is further opened up, the discharge ribbon would have to take in more laminae and be thicker, so as to make up the cross section required for discharge.

In the construction of a pump of commercial form there are practical considerations which heretofore have not been met without serious compromises, such compromises showing so great an interference with theoretical considerations that the efliciency does not approach the ideal.

First, in any'commercial pump the throating must be initially fixed as great enough in size to permit outflow of the full discharge at maximum capacity for which the pump is designed. Second, while the water is within the control of the impeller and the casing, the'relation of pressures according to the square of the radius is fairly well maintained, but the moment that the water leaves .the impeller and therestraint of the circular guiding channel is lost and the water passes into a throat, the pressure throughout the cross section of the outwardly flowing stream must be equalized. Third, the motion of the liquid within the pump casing and channel is not a simple or single motion. The movement of the particles of water is very complex, particularly during the acceleration of liquid when the pump is pumping.

disturbing factor in and of itself. The prior art has provided no means for overcoming difliculties produced by the ports themselves, in the following respects:

1. As the impellerblades pass over the ports the blades set up eddies and disturbances in the throat because the contents of the throat are displaceable.

2. As liquid tends to leave the-impeller to pass into the throat, the layers of water which theoretically are maintained in the impeller and casing are no longer .segregated, as would be de- 'sired in the ideal pump. Instead, liquid from widely different layers is permitted to enter the port, causing violent disturbance in attempting to equalize the pressures at difierent points in the throat. a

3. The particles of water at the maximum radius have maximum energy and when they enefliciency will be reduced by the necessity for equalization of the high energy liquid with 'liq-' uid of lower energy than is required for making up the discharge.

Heretofore the prior art has attempted to remove the outermost or high energy water by a succession of throats of small capacity, operating a good deal as a plane does upon aboard to take off a shaving from the outermost periphery.

' This has been conceived as the most efiective way of trying to get a high energy liquid drawn oil? at the periphery through multiple difiuser ports and then equalized in a channel or manifold prior to discharge.

According to the present invention, I have departed completely from the theory of the multiple throat difiuser and have provided a single throat capable of taking ofi a ribbonof waterof variable depth according to the rate of permitted discharge, but always allowing the water of high energy to take first place in making up the discharge, so that upon equalization'of the pressure of successive laminae of the ribbon forming the discharge the highest mean effective pressure in the throat for any particular discharge will be secured.

The ribbon of liquid'which is to be taken off of the periphery of the rotating mass of water is not a solid rigid body and a part of my discovery resides in the realization that to take a thin shaving of liquid in the form of a ribbon ofi of the periphery does not require that a slot or throat like the slot or throat of a plane be disposed transversely across the width of the rotating mass in order to secure a ribbon which consists of the outermost layers across the peripheral face of the revolving mass of liquid.

, According to my present discovery, the outermost layer of liquid which is required for making up the discharge-any discharge within the capacity of the pump-may be drawn off in an orderly manner, that is, with minimum interference between high energy and low energy liquid, by the employment of an oblong longitudinally extending slot by virtueof which liquid v 2,291,478 Fourth, the presence of the discharge port is a than the desired energy, the mean pressure in the throats will be unavoidably lowered, and the flows both longitudinally and laterally into the throat from the outermost laminae, successively, in making up the particular discharge which the pump at any particular point in its capacity may be delivering.

By the provision of a slot or throat of a conventional length and of a width substantially less than the width of the ribbon of liquid which is actively under the influence of the impeller, a blade sweeping over the port is caused to present first opportunity for outflow to the outermost particles of the ribbon which constitutes the discharge, and slightly less opportunity to the particles having less energy, so that no matter what the thickness of the discharge ribbon of liquid, the equalization which is required will be only between the particles of maximum energy, and particles no further away from the outermost or maximum radius than is necessary to make up the thickness of the discharge ribbon. Hence, the mean effective pressure will be,maximum for the particular rate of discharge.

- The relatively narrow throat largely prevents or at least effectively limits endwise disturbance of liquid in the throat that tends to regurgitation as the vane passes over the same. This reduces or eliminates certain losses which have heretofore been unavoidable. The narrow slotlike throat which is disposed endwise of the movement of the blades in eflect allows equalization inside of the channel or casing-independently of equalization on the outside of the narrow slot or opening in the discharge throat. There is only a high velocity connection of reduced cross-section between the two whereby the function of doing work upon the liquid .within the casing, and thefunction of equalization of pressure and producing flow on the outside of the slot or in the throat without mutual interference is promoted.

' efficiency is pronounced.

Hence, the settingv up of unnecessary eddies or motions in the liquid is reduced with increase in flow pressure and efficiency.

This construction is applicable to all the various forms of concentric pumps, both those employing a single throat or a plurality of throats, as shown in my prior Patent No. 2,123,454, or self-priming pumps with a single pair of throats or a plurality of pairs of throats, as shown in my prior Patent No. 2,110,883. The improvement produced by my invention is marked and distinctive. Primarily, the pressure curve is flatter, that is, the pressure remains higher throughout the entire range of deliveries than in any pump of the prior art known tome. Greater delivery within certain sizes as compared with prior practice of those same sizes is now possible. Increased Due to more orderly flow, higher speed of the impeller without the loss of efllciency occurring in the prior art is now possible. A smaller lighter pump and a smaller lighter engine not only of high speed but of less power will now do the work requiring a larger pump and engine of the prior art. In pumps of this type operating. as self-priming pumps the priming is not interfered with and in fact at the higher speeds is made even more eflective than it has been in like capacity of pumps of the prior art.

According to the structure herein illustrated, and which is the preferred construction, the slotlike throat leaves on each side thereof a concentric ledge which constitutes in effect a con clearance, or substantially only mechanical clearance, do work upon the liquid to bring it to a state of maximum energy content at maximum radius. The presence of these ledges along the sides or flanks of the slots performs the dual function not only of distributing the outermost layer of maximum energy liquid along the length of the slot but allows work to be done upon liquid in the channel over these ledges so that the blade in passing from one end of the throat to the other end does not tend to lose all of the high energy liquid but depending upon the design may carry past the throat some of the high energy liquid to a succeeding throat, as in the case of a.

self-priming pump. This is possible because while high energy liquid is sliding ofi into the slotlike throating from the ledge, work is being done upon liquid further along on the ledge and this can be carried to the auxiliary ports to provide high energy liquid for discharge at the auxiliary or priming port. Hence the designer has much greater freedom of ratioing the capacities designing the shapes, sizes, spacing, etc. of the two ports relative to each other than has been possible according to known practice.

The desideratum of high efficiency and maximum available pressure requires that the flow constituting delivery at any particular value within the capacity of the pump be made up of liquid of the highest mean value of contained energy available. In other words, as the delivery increases progressively lower energy liquid must be allowed to enter the discharge but at no point should liquid of lower energy than that necessary to make up the discharge be permitted to .make up the discharge for the reason that first the mean pressure would be needlessly lowered and second the work of equalization of pressures in the throat would be increased with loss of efficiency.

To secure the desired selective discharge of liquid according to energy content it is simpler to selectively retard the outflow of liquid of low energy content. Bearing this principle in mind, the throat or slot may be shaped variously to ofier relatively free escape selectively to liquid of high energy content by providing greater retardation to outflow of liquid of low energy content. This should function over the entire capacity range to be most efiective. In accordance with this principle the slot or throat may be tapered-in width from a greater width or opening at the front end of the port to a less width at the rear end of the port or throat. The sides may be straight or curved to meet the particular requirements of a specific service.

Now in order to acquaint those skilled in the the characteristics of known forms of pumps prior to the introduction of myinvention;

Figure 6 is a diagram illustrating the energy content of liquid at various radii;

Figure '7 is a fragmentary diagrammatic illustration of the operation of known types of pumps;

Figure 8 is a similar diagrammatic illustration not showing any actual structure but indicating the character of operation of the pump of the present invention;

Figure 9 is a side elevation of a complete pump embodying my invention;

Figure 10 is a vertical section of the pump shown in Figure 9 taken on the line l0l0 of Figure 9;

Figure 11 is a horizontal cross section of a pump casing employing two pairs of throats;

Figure 12 is a developed elevational view of the throat opening taken on line l2-I-2 of Figure 11;

and

Figure 13 is a view similar to that of Figure 12 showing a developed elevational view of a modified form of throat opening suitable for use on a casing such as that shown in Figure 11. I

The pump herein illustrated was developed for the practical requirement of a fire pump for a portable fire pumper, the embodiment of the pump of the present invention in such a pumper being 'illustrated in my copending application Serial No. 293,227,,fi1ed September 2, 1939.

According to the requirements of that particular service a compactlight weight unit of large delivery capacity, that is, large gallonage, i. c. 150 g. p. m., and capable of delivering a 'pressure of the order of IQ!) pounds per square inch is needed. Overall efficiency is of the highest desirability, since it is particularly necessary for small size and high speed. It is desirable that the pump be operated at a high speed in order to be able to employ a small size high speed motor, and thereby to hold down the size and weight and incidentally the cost for making the pumper above referred to. The pump must, furthermore,

be highly efiective on self-priming, so as to avoid all delay in priming and to be capable of taking its liquid from almost any reasonable source and holding up its pressure even though there should be air leakage into the intake.

The general features of the pump are indicated in Figures 9 and 10. The pump is of the open impeller type having the impeller I l with a shaft as hearing blades I! which run in a channel the 7 side wall of which is indicated at l3 in Figure 10,

art with the manner of constructing and operating a specific embodiment of my invention, .1 shall describe, in connection with the accompanying drawings a preferred embodiment, its mode of operation and use.

In the drawings:

Figure l is a vertical cross section of a selfpriming pump of the type employing a single pair of throats and embodying my invention;

Figure 2 is a section taken on the line 2-2 of Figure 1 showing the throat section through the main throat of the pump shown in Figure 1;

and the cylindrical peripheral wall of which is indicated at M.

The impeller casing 13 has two adjacent substantially tangential discharge passageways comprising the main passageway i6 and the auxiliary 'or priming passageway ll, these two passageways I being divided by a dividing wall l8 between them.

The inlet to the impeller II is through the center, that is, axially, and in the present instance this axial inlet includes a trap 20 with an intake opening 24. The discharge of the pump which includes the passages IB and I1 is directed through-a separator 22 which has an outlet 23 at its top forming the actual discharge connection of the pump as a whole. The functions of the trap and separator in this construction are to constitute the pump a self-priming pump, according. to the invention disclosed and claimed in my prior Patent No. 1,578,236.

The separator 22 during priming provides the necessary space for allowing the mixture of gas and liquid which is formed in the impeller chamout the passageway Hi to segregate into its constituents, namely, as and liquid, the gas passing off through the outlet 23 or through a bleeder port which may be disposed in the top of the separator. is permitted to return from the separator 22 through the return passageway ll peripherally Liquid which is largely freed of air,-

into the impeller H to be converted into mixture and again discharged through the passageway Ii into the separator. uation continues until the pump receives liquid,

. whereupon the pressure created upon the throat of passageway l1 stops recirculation, reverses flow and constitutes passageway ll an auxiliary discharge passageway.

The separator 22 and the pump casing l5 are joined preferably by bolting flanges 2I-2i re-" spectively, The separator has companion p'assageways i6 and i1 corresponding to the passageways i6 and I1- and forming continuations of 10. This action of air evac- Iii-order to provide the higher pressures, greater compactness and better efliciency and to permit higher impeller speeds, desired for this serviceas well as for general purposes, I have devised the novel mode of discharging the liquid which is the subject of the present invention.

It is to be observed that the invention is not limited to self-priming pumps, but is applicable to non-self-priming pumps, both of the single and plural throat type. The invention shows particular utility in multi-throat pumps, such as the self-priming pump of my Patent 2,110,883. It may also be employed in the multi-throated nonpriming pump of my prior pump Patent No. 2,134,254.

The specific form of the impeller is not of th essence of the invention. I have found that the open impeller with substantially straight blade is the most desirable. .The straight type of blade effects priming more rapidly than does a blade of pronounced curvature. This is particularly true in pumps employing .a single outlet for 2,291,478 7 her by rotation of the impeller and discharged 1 enough to discharge the mixture and avoid over compensation. Also during liquidpumping the main passageway I6 does most of the work since it receives and removes liquid upon which maximum amount of work has been done in advance of the auxiliary or primirm throat IT. The priming throat presents the problem that it must be of suflicient capacity to return an adequate be avoided or overcome, otherwiseefliciency suf-.

fers.

Referring now to Figiire 6 which is a diagram for explaining the energy content of liquid within the pumping channel or pumping chamber, assume that a cylindrical channel with suitable side walls-is defined by the circle a, the center of which is at 0. A vertical radius 0, 1, represents the effective radius of an impeller blade working within the channel whose inner periph ery is defined by the circle a. It may here be stated that the clearance which exists between the impeller and the side walls of the casing of the present pumpis intended to be substantially only mechanical clearance and to prevent solid particles which might be carried in the water from wedging into the gap and cutting the blade and casing. Hence, a clearance of 3 2 inch on each side is satisfactory for pumps of the present type and for the pump herein lets for mixture the relative carry of the mixture is shorter and particularly with the improvement herein disclosed. The mutliple throat selfpriming pump may employ an impeller with a pronounced curvaturer This gives the designer much greater freedom of design as it allows the development of various pressures within a given radius of blade.

The front faces of the impellerblades are surfaces substantially normal t the plane of rotation of the impeller. That is to say, they have no functional bias to either side of the impeller cas- 'ing. Such impellers are old and well known in shown. The tip clearance on sizes like that of the impeller herein shown, which impeller is,

by way of example, 9% inches diameter by inch width, may be from a to /2 inch, and in larger sizes of pumps, it may be even as much as 4 inch or more, the purpose of the clearance being largely to avoid injury from liquid-borne solids. Even with those clearances, it is considered that the liquid at the outer periphery is entirely withinthe influenceof the impeller and moves with it.

Referring again to Figure 6, assume a particle which may be laid 'ofi on the horizontal line 1', :c, as, for example, four units of velocity corresponding to four units of length of the radius. The straight line 0, b, represents proportion.- ately the velocity of any particle of liquid at any particular radius along the length of the blade 0, r, and this is indicated by the small letter 22 as the four units of velocity corresponding to four units of length of the' radius. Now

if we consider the energy content of the particle of liquid at the end of the radius 0, r, it will be realized that this is proportional 'to the square of the velocity, as indicated by the length of the line 12 The curve 0, c, indicates the energy the high energy particles at the very periphery and of the particles of lower energy at a shorter radius is equalized only by the high energy being expended in eddies or useless motion of equalization, the mean pressure in the throats may be more nearly that of the lower energy particles which enter the throat than thatof the higher energy particles. Eddies and parasitic motion in the liquid are to be avoided at every point. Sharp differences in energy content tend to set up such parasitic motion and eddies. Also, it can be seen that if lower energy particles are P rmitted to enter the throat from a shorter radius than is necessary to make up the full ribbon of discharge, not only is the necessity for equalization increased because of marked dif ferences in energy content, but the mean effective pressure of discharge will be reduced.

Now it is the purpose of the present invention to take off the laminae in the order of their energy content, and to equalize them with a minimum of shock and useless motion in producing discharge outflow. Referring to Figures 1 to 4, inclusive, Figures 1, 2.and 3 show in full lines the structure of the throating of a preferred form of pump embodying my invention. The main discharge passageway 16 opens into the periphery of the channel wall i l through a relatively narrow slot or opening 25, a developed view of which is shown in Figure 3. Theport or opening 25 is the narrowest part of the con nection between the inside of the impeller casin and the separator. In other words, the port 25 forms the greatest constriction of the passageway !6. The throat I6 from the opening 25 expands smoothly and relatively gradually into the The dotted lines 21, 21 on Figure 3 merely indicate the expansion of the throat or passageway [6 in the background behind the opening itself, since Figure 3 is a view from the face of the opening, as indicated in Figure 1, on line 3-3.

Now by way of illustrating the distinction and the importance of the invention, I shall refer to separator 22 so as to reduce the velocity of fiow smoothly and gradually to give the proper reduction in velocity in the separator whereby separation of gas from the liquid is facilitated. Figure 2 shows a longitudinal section through the passageway 16, and here it can be seen that the port or opening ,25 is the narrowest part of the communication between the impeller chamber and the separator 22 along the entire periphery of the pumping channel as defined by the concentric channel wall it, with the passageway IE, and as above stated, constitutes the most restricted part of the passageway it. The significance of this is that the port 25 is the point of maximum velocity of flow through the passageway 16, and it is the point of maximum velocity of new of liquid in the pumping channel. These two velocities being related, it then remains to coordinate them to produce and inv sure an orderly fiow. This coordination is compelled by the shape and size of the port 25, and its relation to the channel and impeller blades as herein described which insures delivery of liquid in the order of energy content thereof. It results thereby that maximum velocity delivery and consequent maximum delivery head is available at each delivery rate.

the prior practice in pumps of this character or type. In Figure 2 I have shown in'dottedlines 18, 28 the character of the throating forming the communication between the impeller chamber and the separator to define the main throat and passagewaycorresponding to the passageway 16 of Figure 1. The plan view of Figure 4 shows an opening of the type found in the older art and viewed as though taken along the line 3-3 of Figure 1. Now whereas for a inch width impeller, as shown in Figure 2, it was previously the practice to have this throat at its narrowest portion of the order of if; inches in width, and of the same length as that shown in Figures 1 and 3. The width of the throat shown in Figures 1, 2 and 3, in full lines, is A inch, leaving thereby a ledge of 1 6 inch in width on each side; a contraction of the narrowest part of the throat of from representing the width according to the prior art and as illustrated in Figure 4, to approximately 42% according to the specific example of the invention shown in Figures 1 to 3. In other words, the area of the narrowest part of the throat, according to the specific embodiment of the present invention here shown, is of the order of 42% of the cross sectional area of the throat of the prior art. I do not mean to limit the invention to that particular ratio of reduction, since the reduction may be greater, and the improvement of my invention will appear in useful degrees even though the proportion of ledge area to active area. of the impeller is not as great as that illustrated in this specific instance. The optimum ratio of port width to blade width or channel width may vary with factors such as speed, diameter, blade width, clearance, density of liquid and certain other factors, but in general limiting or reducing the port area in amount and shape so as to produce in efiect a restriction to the outflow of low energy liquid is an improvement of great practical importance.

The preferred form above referred to is such as to produce lateral flow into the slot-like throat and to permit work to be done upon liquid along restricted discharge for the liquid of lower energy.

Also, it will be apparent that the channel need not have a cylindrical bottom. It might be curved or V shaped.- That is not the distinctive feature. Also the ledge could at least theoretically be in the center instead of along the sides, or it could be along one side only. On larger size pumps, the throat need not be a single slot. It might be several slots side by side or staggered, with ledges along one or both sides of each slot to secure the action which is herein disclosed.

I shall now refer to Figure 5,Which shows curves indicating the difierence in performance secured by the utilization of my invention. The comparative test was made between a pump of the prior art showing the throat characteristics of Figure 4 and the same size pump with the throating of Figure 3. The pump with the known form of throating shown in Figure 4 was a size enemas in sc far as constituting the maximum constrlction between the impeller chamber and the pak" .sageway l1, and comprising a relatively narrow slot of conventional length, securing the actions R. P. M. as 21 seconds, which equals 1.9 linear j feet per second. I The dry vacuum which this pump was capable of drawing was 28 inches of mercury or 31.7 feet at an elevation above sea level of 46 feet. The curve plotting pounds pressure against delivered gallons per minute of the known form of throating is labeled old." It' shows a rapid dropofi of the pressure as the gal-.

lonage of delivery increases to 150 gallons per minute.

A similar test was run upon anew form. of

- pump of the same size 20 Type F1. The impeller second, and the pump showed the same dry vacuum of 28 inches of mercury or 31.7 feet at an elevation-of 746 feet above sea level. Pounds pressure of delivery was plotted against discharge gallons per minute and the curve is marked fl w."

The improvement, as demonstrated in the curve, produced a higher initial discharge pressure and a higher discharge pressure throughout with a very pronounced increase in the cadisclosed in Figure 8, and partaking of the overall improvement of the pump shown in the curves of Figure 5. Y

While I am 'not able to say from direct observation, since I have not found thatpossible, just exactly what the action is which makesthe throat shown in Figures ,1, 2 and 3 operate at such a high efliciency, I' believe that the operation is as pictured in Figure 8, and I know from actual tests that the improvement exists and is very pronounced, as illustrated in the curves of Figure 5.

By this scheme of forming the port as a longitudinal slot, the high energy layer is distributed along the entire length, rather than being dumped over the front edge, as shown in Figure 7. Likewise each succeedinglayer is strewn along the length of the slot rather than successively dumped in. Since the slot or opening 25 forms the maximum constriction the velocity is therein the highest of any part of the discharge pa'ssageway. v The result of this high velocity movement through the narrow slot is a tendency to segregate the action within the channel from theaction within the throat beyond the slot, so that equalization or re-arrangement on one. side of the slot will less affect the conditions on the other side of the slot than has been the case in structures of the prior art. Pumps embodying this form of throating and this mode of operation are quieter and more efficient than pumps of the pacity of the pump and a pronounced increase in Refer ing new to Figure 7, assume the blade I! is moving towards the conventional prior art port 29 which is shown as open across the full width of the 'channel M. It will be seen at once that the higher energy liquid at the maximum radius can immediately spill into the opening. and since the port 28 is freely open for its full length this introduction of high velocity liquid all into one end of the throat creates an immediate high velocity flow and a resulting disturbance, because of the great difference in energy content of the liquid in the throat. Some of the liquid tends to eddy and'escape back or,'force other liquid back into the pumping channel. There is nohigh energy liquid at the other end of the throat in Figure 7 to prevent the pulling in of low energy liquid by the initial high energy discharge.

Referring now to Figure 8, a section of the channel employing my invention is indicated, the ledge 26 in this case being exaggerated so as to make clear the effect which I believe is secured by the present construction and mode of opera tion. Some of the high energy liquid from the maximum radius is immediately-spilled into the throat opening 25. But, owing to the presenceof the ledge 26, liquid at maximum'radius and with vhigh energy content, tends to be pushed along on for the passageway I! (see Fig. 1). The port 30' is preferably constructed similar to the port 25,

prior art. The improvement which this inven-'.

tion secures is not limited to a single throat or a two-throat. pump, as I have demonstrated its usefulness in the multiple throat self-priming pump of Patent-No. 2,110,883. a

In the specific pump herein illustrated in Figures l, 2 and 3, and on which the curve marked "new on Figure 5 applies, the length of theslot is substantially identical with the length of throats of the prior art, as may be seen by comparison of Figures 3 and 4. The width, however, is very much less. In the specific pump which I have shown, the ratio of length of the slot to the width thereof is of the order of between 5 and 7 to 1, and the ratio of the impeller width to the throat width is of the order-of between 1.25 and 2 to '1. p

The pump illustrated in Figures 1 to 3'and employed in the test illustrated by the curve new of Figure 5 utilized an eight bladed open impeller 9% inches in diameter, inch wide with inch side clearance, inch top clearance, and a port length on the inner periphery of 3& inches with the edges rounded.

I do not wish to confinemy invention to these proportions or dimensions, as the specific form herein illustrated is by way of example only, and

the presence'of my invention in a pump is determined by thev law of operation and method, rather than by any specific dimension.

Obviously, to facilitate liquid flowat high velocity, the comers of the ledges may be rounded, but the rounding of the comers does not detract from the ability to hold liquid up to the impeller to have work performed thereupon, nor does it detract from the ability of the ledges to distribute the liquid of high internal energy lengthwise of the ports instead of permitting the dumping of the same into the open throat.

I would further point out that I do not intend to limit the length of the slot to exactly the same length as that of prior art practice, but this dimension may also be varied within limits, depending upon a variety of factors such as diame ter, speed, relativewidth of the impeller blade, density of the liquid operatedupon, etc.

A surprising feature of the present invention is that with the new throating and mode of discharging the liquid a reduction in the width but not the length of the throat has not caused a reduction in capacity, but, on the contrary, has

actually increased the capacity of, for example, a certain size of pump. In a multiple discharge self-priming pump of the type known as Type R, of the general character shown in Patent No. 2,110,883, the pump as constructed with full width main and priming throats showed a maximum working capacity of 100 gallons per minute with a head at that capacity of approximately 6'7 feet. The width of the throats at the 67 foot head was inch. I reduced the width of all the throats to inch retaining the full width of the impeller which was inch and kept the length of the slot the same as it was before. The working capacity remained at 100 gallons per minute, but the head jumped from 6'7 feet to 88 feet.

In Figure 11 I have shown in cross section a pump casing of the type known as Type R, having two sets of throats, each set consisting of a main throat 3| and an auxiliary throat 32, communicating at their outer ends with a separator space and at their inner-ends through ports 33 and 34, respectively, with the channel in which the impeller operates. The impeller 36 is substantially of the same construction as shown in Figure 1, but it may be of either straight or curved blade, depending upon the pressure desired. The port 33, shown in developed elevation in Figure 12, is a substantially parallel-sided slot of which the front end 31 is slightly narrower than the rear end 38. The passageways 3|, 32 provide gradual expansion in cross sectional area,

and thereby reduction in velocity of liquid being discharged. The specific proportions shown in Figures 11 and 12 are of a diameter impeller operating at 3400 R. P. M., the blades of the impeller being /2 wide and having approximately clearance on the side, and the port or slot 33 being approximately wide, whereby the port occupies substantially less width than the full width of the channel and, in fact, less width than the width of the impeller blades.

In Figure 13 I have shown a form of discharge port 33a in which the forward or leading part 31a of the port opening has been slightly enlarged to produce, in efiect, a port tapering in width from the widest portion at the front end 31a to a less width at the rear end 38. In this particular example the widest part of the port at the forward end 31a was 1%", that is, approximately the same width as the channel, and this tapered with converging sides to approximately the point 39, from which the sides were parallel and the width is Thus, for a total length of the port of about 2%", the last 1" was a parallel sided slot wide and the forward part of the slot was tapered. Obviously the taper could be extended the full length of the slot if desired.

The form of port opening shown in Figure 13 showed a marked superiority over the opening of the form shown in Figure 12, and both forms showed a great improvement over forms employed in the prior art practice. It will be observed that the slots are relatively long for so small a diameter of impeller. This impeller, however, was operated at a high speed, that is, 3400 R. P. M.- The ratio of length to mean width of the slots shown in Figures 12 and 13 is of the order of between 6 and '7 to 1.

I do not intend to be limited to the specific details shown or described, nor to the dimensions and specific proportions herein illustrated and described. except as the same are recited as essential in the appended claims.

I claim:

1. In a centrifugal pump of the type having an open impeller with an axial inlet and wherein the pumping channel is concentric with the impeller blades and the impeller blades sweep the channel with substantially not more than mechanical clearance, the front faces of the blades being surfaces substantially normal to the plane of rotation of the impeller and wherein the discharge occurs through a port forming an opening in the channel, the improvement which consists in constituting the port a slot of less width than the impeller blades and of a circumferential length substantially greater than the width thereof, the bottom wall of the channel forming a circumferentially extending ledge along the side of the port restraining radial travel of the outermost layer of liquid operated upon by the impeller blades and permitting work to be done by the impeller on liquid restrained by said ledge along the edge of the port, said bottom wall of the channel having an uninterrupted concentric portion in advance of the port and the port constituting the most restricted part of the discharge passageway.

2. The improvement of claim 1 characterized by the provision of a ledge along each side of the port.

3. In a self-priming centrifugal pump of the type employing a concentric pumping channel with an open impeller the blades of which sweep the channel with substantially no more than mechanical clearance and having a separator chamber between which chamber and the channel there are disposed one or more main passageways and one or more auxiliary passageways, the front faces of the blades being surfaces substantiallynormal to the plane of rotation of the impeller the improvement which consists in the main and auxiliary passageways opening into the channel through ports which constitute the most restricted section of the corresponding passageways, said ports constituting slots of a length substantially greater than the width thereof and being of a width substantially narrower than the ends of the impeller blades, whereby along at least one side of the corresponding port a concentric ledge is formed. the impeller thereby being capable of doing work at maximum radius upon liquid restrained on said ledge and whereby the mean pressure in the corresponding passageway is raised materially.

4. A centrifugal pump having an open impeller, a concentric casing with a channel swept by the blades of the impeller, one or more discharge ports in the bottom of the channel, each port opening into a rapidly expanding throat the port conventional forms of pumps for a wide range of deliveries.

. 5. In a self-priming centrifugal pump of the concentric channel type employing an open impeller with blades which sweep the surface of the channel, the blades having front workingsurfaces substantially normal to the plane of rota-.

tion of the impeller and wherein .there are one or more pairs of adjacent throats consisting of a main throat in advance of an auxiliary or priming throat and a separator chamber to which both throats are connected the improvementv which consists in narrowing the width of the main throat to substantially less than the width of the channel whereby a ledge is formed along at least'one side of the main port to carry liquid at maximum radius under the influence of the impeller past the main throat over to the auxiliary or priming throat.

6. In a self-priming centrifugal pump of the concentric channel type employing an open impeller which sweeps the surface of the channel and having blades the front working faces of which constitute surfaces substantially at right angles to the plane of rotation of the impeller -and wherein there are one or more pairs of adjacent throats consisting of a main throat in advance of an auxiliary 'or priming throat the improvement which consists in narrowing the width of the main throat to substantially less than the width of the channel whereby a ledge is formed along one or both sides of the main port to carry liquid at maximum radius under the influence of the impeller past the main throat over to the auxiliary or priming throat, and wherein the auxiliary or priming throat is substantially narrower than the width of the channel whereby a ledge is formed along at least one side of. the auxiliary or priming throat, the impeller thereby working upon liquid at maximum radius along the side of the throat and increasing the mean pressure in the throat.

7. In a centrifugal pump having an open impeller, a concentric channel with a discharge porttormed in a part of the periphery thereof, said port. comprising a slot of a width substantially less than the width of the impeller blades, and having a ledgealong each edge of theslot, the slot being of a length approximately seven to five times as great as the width thereof, the port forming the innermost and most constricted part of an expanding discharge passageway, whereby the. impeller blades may move liquid at maximum radius into the slot from the front and sides thereof to reduceregurgitation of liquid at the remote end of the slot as the blade approaches the forward part of the slot.

ii. In a centrifugal pump having an impeller I chamber of the concentric type having an open impeller with blades the front surfaces of which i are substantially without inclination to the plane of rotation of the impeller, a channel in which said blades move, said channel having an oblong tangential discharge port of a mean width less than the width of the channel, and of a length 

